There are DiY videos for going the cheaper route and just buying a large CO2 canister that will last you a couple years and hook it up to the same device after buying a couple valves. It's on my project list after I finish my kitchen reno.
Not sure where you are but most big grocery stores will have them at the front or the meat department in a special bin. just ask for how much you want and they dish it out. i know ralphs/kroger/staterbrothers should have them.
